Design of Twisted String Actuated Flexure Joint for Supernumerary Robotic Arm for Bimanual Tasks

Supernumerary robotic limbs (SRLs) have become an effective method for assisting poststroke patients in their daily life activities. However, conventional SRLs are constrained by functionality, wearability, and portability limitations, which are attributed to the presence of bulky robot actuators, gears, complex design, and high-power consumption. This article presents twisted string actuated flexure robot joints (FRJs) for a supernumerary robotic arm (SRA). This design aims for a compact, lightweight, energy-efficient, affordable, wearable, and portable SRL. The twisted string actuation replaces the bulky actuator and gearbox in the robot joint. The FRJ joint design and modeling are proposed for the twisted string actuator (TSA) FRJ and verified through experimental validation. A prototype of the three-degree-of-freedom (DoF) SRL was developed, weighing 2.5 kg and possessing a payload capacity of 0.15 kg. The TSA-driven FRJ can produce 3-Nm joint torque at the cost of 32.5-mNm maximum motor torque, and the full SRL's power consumption is 40 W. In addition, a demonstration of bimanual tasks is presented using the proposed SRL to check its feasibility. Furthermore, the proposed SRL has merits compared with the existing SRLs in the literature.